Comparative evaluation of different rock mass and slope mass rating systems for road cut slopes along National Highway 7, from Rudraprayag to Joshimath in Uttarakhand, India

Abstract

The Himalayan Mountain ranges are very sensitive to geohazards like landslides, earthquakes, cloudbursts, and flash floods because they are known for their neotectonics activity. The geomechanical behaviour of road cut slopes along National Highway 7 (NH-7), from Rudraprayag to Joshimath in the Garhwal Himalayas, is significantly influenced by lithological diversity, tectonic discontinuities, and external triggering variables like seismic activity and precipitation. This study conducts a comprehensive comparative analysis of multiple rock mass and slope mass classification systems, specifically Rock Mass Rating (RMRbasic), Slope Mass Rating (SMR), Continuous Slope Mass Rating (CoSMR), Chinese Slope Mass Rating (CSMR), Geological Strength Index (GSI), and Q-slope, across 18 selected slope sections with diverse lithologies. Kinematic analysis via stereographic projection discovered failure modes, revealing planar, wedge, and toppling mechanisms associated with joint orientations and slope geometries. CoSMR, which incorporates continuous functions for adjustment factors (F1, F2, and F3), offered superior resolution for stability classification relative to conventional SMR and CSMR techniques. The RMRbasic values varied from 33 to 73, with quartzite and gneissic slopes demonstrating elevated stability indices, whereas phyllite, dolostone, and slate slopes were categorized as severely unstable due to diminished RMRbasic, GSI, and Q-slope values. The Q-slope approach, which integrates environmental influences and stress reduction factors (SRF), yielded Q-values ranging from 0.01 to 0.25, facilitating the calculation of critical slope angles by Barton’s empirical formula. The results indicate that CoSMR provides enhanced accuracy in intricate terrains through its continuous parameter scaling, whereas Q-slope yields reliable forecasts for slope angle stability across different probabilities of failure (PoF). This work offers improved geomechanical understanding for optimizing slope design, excavation techniques, and stabilization strategies in seismically active and rainfall-prone areas of the Himalayas.